The role of peritoneal macrophages as accessory cells in antibody formation is to be studied in the light of the functional heterogeneity of these cells. Their separation from the bulk of the peritoneal macrophages and further division into cells responsible for formation of informational RNA and RNA-antigen complexes is proposed. Target cells that respond to these two immunogenic entities are to be identified. The mechanism of formation of RNA-antigen complexes will be examined further in a cell-free system which already has yielded suggestive evidence for an important role of enzyme(s) in the production of imunogenic complexes. Other studies will seek to establish the relationship between informational RNA and m-RNA. The transfer of allotypic markers expressed on H and L polypeptide chains of antibody molecules will be used to supplement the studies on i-RNA, and this work is expected to shed new light on antibody synthesis and the function of i-RNA. We shall also employ i-RNA in studies on the relief of allotypic suppression. Cell cultures will be employed. The methodology to be used is tissue culture, cell separations, induction of i-RNA and RNA-antigen complex formation, extraction and purification of RNA, assay and characterization of antibody as to class and allotypic specificity as previously employed by us or others in related studies.